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Since the map is in Alaska, you can use Garmin's "report map error" page to report the map error. They may (or may not) fix it for the next release. Just for curiosity, how much are the maps shifted. In North America, I have occasionally seen shifts up to tens of meters. In China, the shifts are in terms of several hundred meters.

Maybe i will try the error report. The only contact i had with them was through support and all they told me to do was to do a master reset my gps which i know isn't the problem since 2 of my friends had other garmins and their tracks were off too. 2 of us have older sirfstar units and one has 1 yr old garmin H receiver unit.. The problem is in the maps which can be off from 50feet to 100+ meters. it's nuts. setting it to lock on roads will show it properly on the display but that's gotta be an artificial view where it forces you to track on the image's road lines even though that's not where it wants to put you. It shouldn't be that far off with the road lock disabled.

Originally Posted by syzygy

Just checked the Google road and satellite maps in Alaska and you are right. While both maps match in Anchorage, they don't match in Fairbanks (located about 360 miles north of Anchorage).

If the map you have is in OF format, you can open it with GPSMapEdit to edit it to your heart's content (may need to unlock it first). But if the map is in NT format then your are out of luck. There is no tool to open and edit an NT map today. You can only report the errors to Garmin/Navteq and wait until they are fixed.

Now that i know about the error thing, i will try it. It's been 2, maybe 3 yrs since i emailed them where they assumed it was my gps. You're right about Anchorage being okay, you're also okay if you stay on the 1 or 2 main highways that run through the state, once you stray from them even a little, the maps are wonky. My maps are NT so i guess i'm out of luck there. What's OF format? It might be good to pick spots and fix them just to have some proper maps.

The problem with the maps is they are off and that puts the whole gps into question if i'm wandering through the forest or out on the water or where ever with no visual landmarks...am i really where it shows I am?

What's OF format? It might be good to pick spots and fix them just to have some proper maps.

OF stands for Old Format or Original Format. It is the Garmin map image file format preceding NT format. I have only seen OF used by Garmin China and Garmin Taiwan to distinguish maps in old format from the new NT format. See an example below. Here in Noeman, it is otherwise referred as Non-NT.

If there are not many changes in your area, you may want to find an old map of your area in OF format so that you can open and edit it, add new roads and POIs if necessary. By that you can have a corrected and updated map of your area.

As i understand the shifting is not static. Is there an algorithm to get the correct values or is whole china virtually tiled and there is a database with different correction values for every tile?

That's right. The shift is location dependent. Let (x, y) and (x', y') be the original and shifted coordinates respectively, then

x' = f(x, y)
y' = g(x, y)

where f and g are two un-published functions strictly controlled by the Chinese government. The shifts x'-x and y'-y oscillate like a wave in each direction. Although there are many ways to find, fit or approximate f and g, no one wants to break the law by publishing a high precision version of f and g.

That's right. The shift is location dependent. Let (x, y) and (x', y') be the original and shifted coordinates respectively, then

x' = f(x, y)
y' = g(x, y)

where f and g are two un-published functions strictly controlled by the Chinese government. The shifts x'-x and y'-y oscillate like a wave in each direction. Although there are many ways to find, fit or approximate f and g, no one wants to break the law by publishing a high precision version of f and g.

Then, is it breaking the law to use (or to have a copy of) the Venus map in China?

Thanks so much.
So the only reason for the special chinese Chipsets in the Navs is to protect these two functions?
Harder to analyse a chip than to debug a special firmware?

As far as I know, there is no special chipset required. f and g are implemented in the navigation application (firmware or executable file) or plugin like 006B082300.bin today, probably to save cost. Of course, this makes it easier to reverse-engineer the f and g.

Originally Posted by cwhlam

Then, is it breaking the law to use (or to have a copy of) the Venus map in China?

May be. Each Venus release in China has the following disclaimers which I did not bother to post here.

* There is certain risk to use maps in this series. Think thrice before using it.
* There is no warranty or guarantee provided for using maps in this series. Please bear the consequences by yourself.
* Maps in this series are for research and education purposes. Please delete the files in 24 hours after downloading.
* Please consult your lawyer beforehand for all legal issues regarding the use of shift-corrected maps.

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